Pharmacology lecture 4 0.0 / 5 ? BiologyDrug interactionsUniversityNone Created by: willmiddlehamCreated on: 27-03-15 14:42 Does an antagonist have efficacy? NO - AR* does not exist 1 of 15 What does a competitive antagonist do? Binds and prevents (competes) agonist action but can be overcome with an increased agonist concentration 2 of 15 What effect does a competitive antagonist have on a agonist-response curve? It causes a parallel shift to the right 3 of 15 What does a irreversible competitive antagonist do? Binds and forms irreversible covalent bonds with receptor 4 of 15 What effect does an irreversible competitive antagonist have in an agonist-response curve? Causes a parallel shift to the right and reduced maximal asymptote 5 of 15 What does a non-competitive antagonist do? It blocks downstream responses eg. Ca2+ influx 6 of 15 What effect does a non-competitive antagonist have on a agonist-response curve? It decreases the slope and max of the curve 7 of 15 What is the dose ratio? (Agonist + antagonists EC50)/ agonist EC50 8 of 15 What is the Shild plot for a competitive antagonist? r-1 = [B]/kb r=dose ratio B=antagonist conc kb = antagonist dissociation constant Note. Where line intersects x axis = logkb 9 of 15 What does a pA2 value describe? The activity of a receptor antagonist. pA2 = -logkb BUT only if relationship is linear and child plot = 1 i.e.. ONLY a COMPETITIVE antagonist 10 of 15 What is similar to an irreversible competitive antagonist? Weak partial agonists 11 of 15 What is the therapeutic index? Risk:benefit ratio TI = TD50/ED50 or LD50/ED50 12 of 15 What is TD50? Therapeutic dose 13 of 15 What is LD50? Lethal dose 14 of 15 What is ED50? Effective dose 15 of 15
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